The present invention relates to low-cost cochlear implants, and more particularly to a low-cost cochlear implant that artificially stimulates the cochlea as a function of sensed audio signals to improve hearing of the hearing impaired.
Cochlear implant devices and systems are in worldwide use to restore useful auditory sensations to deaf patients. Such devices and systems take numerous forms, as seen, e.g., in U.S. Pat. Nos. 3,751,605; 4,357,497; 4,400,590; 4,408,608; 4,532,930; 4,9118,745; or 5,095,904, all of which typically include an external (or wearable) processor and an implanted stimulator. Such transmission requires generating a carrier signal and modulating the carrier signal with information representative of the sensed and processed sounds. The external processor includes circuitry for sensing audio sounds, processing the sensed sounds in accordance with an appropriate speech processing strategy, and transmitting a signal representative of the sensed and processed sounds to the implanted stimulator. The implanted stimulator includes appropriate electronic circuitry, powered from electromagnetic energy contained within the carrier signal transmitted from the external processor, that receives the transmitted carrier signal, extracts operating power therefrom, demodulates and decodes it, and applies an appropriate stimulation signal to one or more electrodes of an implanted cochlear electrode array. The electrodes of the array are implanted within the cochlea, and when energized cause an electrical current (stimulation pulses) to flow, in accordance with a pattern and amplitude as determined by the speech processing strategy, in order to stimulate the neurons of the auditory nerve. Such stimulation imparts to a patient the sensation of hearing. Performance of some patients who use such cochlear stimulation systems is good enough to allow conversation over the telephone.
Recent advances in speech processing strategies have demonstrated that the level of speech recognition in all implant patients may be significantly improved. See, e.g., Wilson et al., "New levels of speech recognition with cochlear implants," Nature, Vol. 352, pp. 236-238 (1991). Unfortunately, the high cost of present commercially available cochlear implants makes them unaffordable for many patients. What is needed, therefore, is a low-cost cochlear implant device that would allow the recent advances in speech processing strategies to be more widely used and available to deaf patients than has heretofore been possible.
A low-cost cochlear device must not achieve its low cost at the expense of patient safety. In any implanted electronic device several potential hazards exist for the patient. For example, all materials should be fully biocompatible, or otherwise insulated from direct exposure to body fluids. If toxic internal components are necessary, they must be encapsulated in an impenetrable casing (hermetically sealed) to protect surrounding tissue. All manufacturing and construction techniques must be performed in a suitable clean room or laminar flow hood to reduce the possibility of dust or other airborne contaminants from entering the fabrication materials. Further, all components used in the overall design must assure reliable operation over a long period of time, preferably for the lifetime of the patient. As the number of components within the implanted device decrease, these safety and reliability concerns can generally be kept at manageable levels. Hence, it is best for an implantable cochlear stimulator to have a low parts count.
The first goal of any auditory device, of course, is to provide the user with a reasonable level of auditory function. Like most evolving technologies, what is "reasonable" has changed in recent years as the performance of cochlear implant devices has improved. If reasonable speech recognition is defined as 20% correct or better using only sound sensed through the implant for everyday sentences or their equivalent, then a multi-channel device is necessary.
For purposes herein, "multichannel" means that stimulation may be applied to the cochlea at several physically-separated sites, each of which is selectively and independently controlled by respective electronic circuits, or "channels" in accordance with the desired speech processing strategy. It is generally agreed that having multiple channels provides improved auditory response. However, the optimal number of channels to use, particularly in view of the increased cost and complexity of the device, remains an unanswered question.
Multichannel devices should not be confused with single channel cochlear implant devices, such as is shown in U.S. Pat. No. 3,751,605, where the information contained in a single information channel is transmitted and applied to an intra-cochlear electrode. While single channel devices can be made much simpler and less costly than a multichannel device, they only provide some sound awareness and limited speech discrimination. As such, they are primarily useful only as an aid to lipreading. In contrast, present day multichannel devices provide open-set speech recognition in the 30-60% range of most patients, with some patients being able to converse over the telephone with strangers.
Likewise, multichannel devices should not be confused with simple multielectrode schemes where effectively a single channel of auditory information is applied, on a shared basis, to multiple electrodes, such as is described in U.S. Pat. No. 3,449,768. Although the '768 patent refers to its separate electrode pairs as separate "channels," they are clearly not separate channels as that term is used today to describe cochlear stimulating devices. Multi-electrode schemes driven by a single auditory channel of information, such as that depicted in the '768 patent, have long been abandoned as ineffective at producing acceptable speech recognition.
Although some patients with multichannel devices do not perform well, such should not be viewed as an indication of the failure of multichannel devices. Rather, such failure probably reflects the fact that some patients with poor nerve survival, electrode placement, or device adjustment cannot recognize speech even with multichannel implants. Thus, while there is a wide variation in performance for all patients, over 20 years experience indicates that a multichannel implant is necessary to achieve reasonable speech recognition.
Disadvantageously, the use of multiple channels significantly increases the cost and complexity of the device, particularly the implant device. Yet, as indicated above, a multichannel device is much preferred over a single channel device in order to significantly improve the level of auditory function provided by the device. Hence, it is apparent that there is a need in the art for a multichannel device that avoids the complexity and expense of existing multichannel devices, is inexpensive to manufacture and maintain, and is safe to implant and use.
A further contributor to the high cost of cochlear implant devices is hermetic sealing. Any electronic package implanted into the human body must be hermetically sealed to protect the delicate electronic components from the harsh body fluids, and to protect the patient from exposure to potentially toxic chemicals contained in the electronic components. Early cochlear implant devices were encapsulated in silicone rubber, epoxy resin and/or bone wax. These devices lasted for many months (and in some cases years), but all failed eventually because water vapor penetrated through the silicone rubber and epoxy, causing corrosion and short-circuiting of the passive components, and/or failure of the active components.
Hermetic sealing, unfortunately, is a complex technology that is still undergoing significant development efforts in related implantable industries, e.g., the pacemaker industry. Titanium or ceramic capsules are sealed with electron beam welding or laser welding or brazing. The electrical leads coming out of the capsule present a particularly difficult problem for the seal. Each lead must be fully hermetically sealed and insulated from the capsule. This is typically accomplished by conductive pins sealed to ceramic collars which are then sealed to the capsule. Electrode wires are then connected to the pins. Hermetic sealing is one of the most costly and difficult processes used in construction of modern cochlear implants. For a truly low-cost cochlear implant device to be made, either a low-cost hermetic seal must be developed, or the implant device itself must be able to function safely for long periods of time without the need for an hermetic seal.
The present invention advantageously addresses the above and other needs.